Cobalion, Terrakion, and Virizion: Three Pokémon based on the titular characters of the novel The Three Musketeers. Out of these swords of justice, Cobalion is the oldest and wisest and is considered their leader.
Keldeo: The fourth member of the Swords of Justice, thus making them a quartet.
Tornadus, Thundurus, and Landorus: Based on three Japanese gods known as kami, with Tornadus based on Fujin, the god of wind, Thundurus on Raijin, the god of thunder, and Landorus on Inari, the fertility god. Landorus is the master of this trio.
Some of the remaining Legends fit into pairs, namely,